Influence of fuel type and heating approach on one-step microwave combustion design of Zn-spinel as supreme sunlight-responsive nanophotocatalyst for degradation of orange II in water

Abstract

The present research was aimed to evaluate the contribution of fuel type and heating approach as the most significant parameters in the solution combustion synthesis method to provide the appropriate structure of the nanophotocatalyst with substantial properties and consequently, higher photo-degradation efficiency of dye pollutant under solar simulated light exposure. To this target, the Zn-spinel nanophotocatalysts were synthesized via one-step microwave combustion method (MW) using three fuels including ethylene glycol (EG), acetic acid (AA) and glycine (Gly) and two heating approach (microwave and muffle furnace (MF)). The prepared nanophotocatalysts were characterized through XRD, FESEM, TEM, EDX, BET-BJH, TG, H2-TPR, DRS, PL and pHpzc analyses. The photo-degradation efficiency of high-concentration orange II as a widely used textile dye in water was determined over the synthesized Zn-spinel photocatalysts under simulated sunlight irradiation. The characterization results revealed that the mesoporous and spongy-like morphology of Zn-spinel nanophotocatalyst (ZnAl2O4(Gly-MW)) with proper crystalline structure was successfully gained through microwave-combustion synthesis method using glycine. In neutral media (pH = 6), ZnAl2O4(Gly-MW) sample with the catalyst loading of 0.75 g/L during 160 min of simulated sunlight exposure showed the outstanding degradation efficiency (70.2%) of orange II (140 mg/L) which is about 17.6% higher than the sample prepared using the same fuel but with conventional heating method. The high chemical, mechanical and optical stability of ZnAl2O4(Gly-MW) after six cycles was achieved. Furthermore in this investigation, the effect of the dye solution pH on the degradation performance was studied and the degradation mechanism of orange II over ZnAl2O4(Gly-MW) nanophotocatalyst was proposed.